High gas bill - Vaillant 637 - UFH and Alu Rads - Help

[Parmsuk]

Hi,

Following a full refurbishment of an house and a new build rear extension we had a brand new heating system installed. Give you an idea of what it is:

• Vaillant 637 system boiler
• 300l Water tank
• Wet UFH (floor area 15x4m) in new rear extension (family area, kitchen and dining) - used all day (1 zone). Unknown but calculated by SOLFEX from what I recall seeing by the heating engineer at the time.
• Existing Downstairs, existing upstairs each with own zone (2 zones).
• 5 bedrooms (1 guest so hardly used), 3 bathrooms.
• 17 Aluminium radiators in total 25Kw in output excluding UFH (i don't the KW what this actually is)
• Honeywell Evohome with Y87 wall stats in each zone

1 year in and our gas bill seem very high, much more than anticipated. Approx. 45,000Kw used.

I've been many forums over the past week or so and it does seem that my usage is much higher than standard (18Kw-20Kw).

The past week I've also been monitoring evohome and I can see that the UFH once up to heat even in this cold weather spell (-1 degree) it maintains a lovely 19 degrees all through the day with just the odd call every couple of hours for a bit of heat (10% or so) and switches back down to 17 through the night (i can see that it does'nt drop lower than 17.5 through the night using some logging software so no heat demand).

The downstairs zone (non UFH - 9 radiators - approx 14KW - downstairs includes bedroom 5 and ensuite) seems to be running most of the day to maintain a temp of 19.5 degrees. I've witness it "cycling" every 10 minutes or so throughout the day.

This morning, i've changed the D00 setting to 24KW, previously it was set to 37KW and see if that makes any difference.

I also took the following readings if it helps:
Flow temperature is: 75C
Return temperature is: 65C

Should I just wait and monitor our smart meter over the next couple days and see if it as any impact??

I've noticed that the max reading on smart meter shows is 22.84Kw since I've made the change to D00, however it goes down only as low to 6.8Kw.

Any other advice??? Is this to be expected??? Oversized boiler???

Thanks in advance.

 

[gmartine]

Pictures of the system would be helpful, Evo doesn't do weather comp which you should have for such a large residence especially with UFH.

 

[Rob Foster]

some gas meter readings are a good start ..tariff and supplier
..and a historical run down of the gas usage. then we can look at the system as gmartine asks
Centralheatking

 

[SJB060685]

Following

 

[Rob Foster]

Following

ok but I am out doin till later but others are just as good if not better than me at this stuff
centralheatking

 

[SJB060685]

I’m curious as to what the end result is lol.

 

[Parmsuk]

Hi,

Smart Meter readings for month of Jan as follows: 1st jan: 4220 and 31st 4936. 716m3 of gas...converted to KW: 8074.

My energy supplier is Tonik and Positively Green v20 tarif. 2.9p/Kw and 22.37p standard charge.

 

[Rob Foster]

Hi,

Smart Meter readings for month of Jan as follows: 1st jan: 4220 and 31st 4936. 716m3 of gas...converted to KW: 8074.

My energy supplier is Tonik and Positively Green v20 tarif. 2.9p/Kw and 22.37p standard charge.

how many people , and a building lifestyle is handy.
ie how many carpet rats ..wrinklies ..etc like me. ..
do you all leave the building
5 days a week or run a home office...see what I mean ?
centralheatking

 

[Parmsuk]

Three adult and 2 young children.
Occupied downstairs throughout the day. However, from 10-4pm we turn down the standard downstairs heating (radiators) to 19degrees. The extension area is where we spend most of the day (kitchen,dining room and family room) and this is heated by the wet UFH at constant 19.5degress from 6am to 8pm which takes an 2.5 hours in the morning to get the desired temp but then maintains it easily throughout the day into the evening with only a couple of times for gentle heat call.

 

[Rob Foster]

Three adult and 2 young children.
Occupied downstairs throughout the day. However, from 10-4pm we turn down the standard downstairs heating (radiators) to 19degrees. The extension area is where we spend most of the day (kitchen,dining room and family room) and this is heated by the wet UFH at constant 19.5degress from 6am to 8pm which takes an 2.5 hours in the morning to get the desired temp but then maintains it easily throughout the day into the evening with only a couple of times for gentle heat call.

ok ...wow ...so ur system is never off essentially . later We will go over it ..you must be loaded ..but hey
centralheatking

 

[Murdoch]

These temperatures you mention, how did you t take the reading?

 

[Parmsuk]

These temperatures you mention, how did you t take the reading?

The flow temps are from the boiler directly and the room temp are taken from the Honeywell Single Zone Thermostat (Y87RF) placed in each zone.

 

[Murdoch]

The flow temps are from the boiler directly and the room temp are taken from the Honeywell Single Zone Thermostat (Y87RF) placed in each zone.

Maybe get an old fashioned mercury thermometer and get the actual room temp ....

 

[sammathias]

So you technically have the heating on alday every day???

25kw known for rads
KW for ufh needs to be known
KW for 300l invented cylinder (5kw...others can correct me)

So without knowing the output of the ufh. You still need 30kw output on the boiler unless the timings for hot water to come on where different schedules to heating

By rating the output on the boiler to 24kw I think you said it's just not going to heat the house effectively.

 

[Sharp Point]

What’s the insulation levels in the walls/floors , how many square meters of glass in the day room?

 

[ShaunCorbs]

Sounds about right if your in the house all day

 

[gmartine]

Bet no LLH.

 

[Chuck]

Smart Meter readings for month of Jan as follows: 1st jan: 4220 and 31st 4936. 716m3 of gas...converted to KW: 8074.

That's roughly twice the volume of gas that I would have guessed based on your description the house and usage patterns. I'm assuming you're in England not the North Pole, of course.

The two areas I'd scrutinise carefully are:

Firstly, the UFH, in particular what's the specification for the construction of the floor? If there isn't enough insulation under it, or there is two much insulation on top of it, UFH can be a really money-pit.

Secondly, the hot water. How much do you use per day and how is it programmed? Have you got a hot water leak somewhere?

Unless your house is essentially uninisulated or you leave all the windows open the whole time, the amount of gas you are using if it were all dissipated as heating would be baking you all alive. This is why I'm suspcious about the hot water. You might be pouring money down the drain, literally.

There is always the possibility that the meter is faulty and is over-reading. Also, are you sure that your meter is not also supplying a neighbour?

Once you done some basic checks, I suggest you get a heating engineer to do an energy consumption and loss calculation for your house to see how much it should be costing you. They'll also be able to check, approximately, that the consumption rate indicated by the meter matches the rate expected when the boiler is working.

I'm probably repeating stuff others have already because I got interrupted for several hours while typing this answer.

 

[gmartine]

Let's just assume your newly refurbished house is reasonably well insulated and your UFH meets the latests building regs.
Your boiler still won't be able to provide the necessary flow rates at delta T20 to your system without a low loss header or other means of hydraulic seperation, that's why I suspect your boiler flow temps are so high (inefficient) and as a consequence you're burning more gas than you should be.

 

[sammathias]

Or could just have a gas leak

 

[Parmsuk]

That's roughly twice the volume of gas that I would have guessed based on your description the house and usage patterns. I'm assuming you're in England not the North Pole, of course.

The two areas I'd scrutinise carefully are:

Firstly, the UFH, in particular what's the specification for the construction of the floor? If there isn't enough insulation under it, or there is two much insulation on top of it, UFH can be a really money-pit.

Secondly, the hot water. How much do you use per day and how is it programmed? Have you got a hot water leak somewhere?

Unless your house is essentially uninisulated or you leave all the windows open the whole time, the amount of gas you are using if it were all dissipated as heating would be baking you all alive. This is why I'm suspcious about the hot water. You might be pouring money down the drain, literally.

There is always the possibility that the meter is faulty and is over-reading. Also, are you sure that your meter is not also supplying a neighbour?

Once you done some basic checks, I suggest you get a heating engineer to do an energy consumption and loss calculation for your house to see how much it should be costing you. They'll also be able to check, approximately, that the consumption rate indicated by the meter matches the rate expected when the boiler is working.

I'm probably repeating stuff others have already because I got interrupted for several hours while typing this answer.

The UFH is set in a 65mm liquid screed, under which is the celotex insulation all to regs and done professionally and then porceline tiles on top. The UFH in this cold weather does take around 2.5 hours in the morning to get to temp, but what I notice is that it rarely comes on throughout the day (monitoring the heat call from evohome) and back on for a top up 30 minutes in the evening.

The hot water is puzzling me to be honest, it was set since we had the system installed (2 years ago) to come on every morning at between 5-6am. But I have turned this off the timer around a week to see if this had any impact. We still have lots of hot water (no one complained that water gone cold). What I have observed is that occasionally the hot water pipe leading from the valve to the tank is hot so this telling me that the boiler is at times automatically reheating??? or is this the tank automatically asking for the water to be heated as its dropped below a certain temperature?

 

[Chuck]

The hot water is puzzling me to be honest, it was set since we had the system installed (2 years ago) to come on every morning at between 5-6am. But I have turned this off the timer around a week to see if this had any impact. We still have lots of hot water (no one complained that water gone cold). What I have observed is that occasionally the hot water pipe leading from the valve to the tank is hot so this telling me that the boiler is at times automatically reheating??? or is this the tank automatically asking for the water to be heated as its dropped below a certain temperature?

You need to look into this and get it sorted. If, for example, the HW zone valve is jammed open you could have a 'hydronic short circuit', which would explain the small differential temperature between flow and return, which will lower the efficiency of the boiler significantly.

 

[gmartine]

Glad Chuck noticed the low differential, as per my previous posts let's see pic's of your set up or we are all Soding in the wind.

 

[Sharp Point]

Have you a secondary hot water circuit?

 

[Parmsuk]

Have you a secondary hot water circuit?

Just checked this morning, there is a dedicated secondary hot water circuit to feed the 5th bedroom/ensuite (furthest away from boiler). Not sure if the mechanical timer was actually in "timer" or "off" mode as it was half way between. Anyway, it was 8.5 hours behind current time (so showing 12:30am at the point I checked this morning). I've ensured its in the off mode and also moved all the little timer sliders to off position so at least I know its for sure not going to come on now. So i'm now wondering if the hot water circuit was coming on early hours of the morning and also again mid afternoon circulating hot water around and actually causing the water tank to cool down? Its during these periods I've noticed that the temp in HW tank drops and then the boiler seems to turn on itself.

I've been monitoring the gas smart meter reading after the heating turns off for the night and again before it turns on in the morning (I know painful). I've noticed consistently that there is at least 10KW used overnight and according to the smart meter the call for gas around 1am and then again at 5am. Once again around mid afternoon of 5KW, all when there is no demand from heating (i.e. target temp is lot lower than current temp).

Lets see what happens today and overnight and I will feed back. Good spot by the way!!!!

So one of my previous question was, if the boiler temperature does drop will the boiler automatically reheat it???? if so whats driving this??? is it the thermostat on the hot water tank?